The basics of HDTV: A behind the screen look at TV technology

By Jonathan Bearfield, End Equipment Marketing Engineer, Texas Instruments Incorporated

Page 1 of 5

(01/31/2007 2:00 H EST)

INTRODUCTION
Whether driven by Moore's Law or consumer demands, the performance level needed in televisions (TV) today can seem overwhelming. High definition (HD) formats, with 1,080 pixels, driving six-times the amount of data as standard definition (SD) TV formats, managing DTV, Internet protocol (IPTV) and video conferencing broadcasts, as well as processingDolby AC-3, MPEG and other audio formats have quickly become "must haves" for digital televisions (DTV).
On top of the technical requirements regarding audio, video and inputsignal formats, there are several viewing options to from which to select: front projection, rear projection, DLP, LCD, plasma, and CRT. Whether watching TV on a one-inch display built into your watch, or using a projection system display using the whole wall, the combinations of size and performance are almost endless.
DTV BASICS
Even though every TV on the shelf today may seem very different when you look at size, shape, form factor and the basic description that the salesperson just gave you, when you look inside the TV the basic building blocks are very similar.
In general, a DTV can be broken down into less than 10 major blocks; the display (and driver), core media engine, audio decoding and processing, video decoding and processing, tuner, interface block and power supply. The absolute performance demand on each block is defined by the performance level you experience from the comfort of your favorite chair.
 

 
 
Figure 1: Typical DTV System Block Diagram
In Figure 1, we show a basic block diagram for an HDTV that we have taken to the functional block level. Many of the tools needed to develop what happens behind the screen can be acquired from a variety of companies. However, ensuring compatibility while speeding up the design cycle for faster time-to-market can become an issue when trying to tie together solutions from several component vendors. Whether tapping into DLP' technology, DSP-based digital media processors, other core processing solutions, or some other high performance analogcomponents, a high level of integration, flexibility and ease of use are needed for the rapidly evolving DTV market place. Leveraging high-performance audio-video CODECs, graphics acceleration,communications and support are essential for convergent applications designed into and around the home entertainment experience.

(01/31/2007 2:00 H EST)

VIDEO
Consumers often place the heaviest weight on the video experience they have while watching TV. As such, resolution, brightness, contrast and clarity impact just how "real" the experience appears. It is critical for TVs to support multiple ATSC DTV formats, NTSC and PAL decoding, composite and S-Video inputs, and 2D adaptive filtering. As HDTV rolls forward, supporting full HD at 1080i resolution with 3D adaptive filtering will be the standard. In reviewing the video signal chain shown in Figure 1, it is important to select video decoders, analog-to-digital converters (ADC), and video buffers that allow a mix of performance capabilities so you can tune the performance to the systems cost target.
 

 
Figure 2: Decoder Data Flow Block Diagram
Figure 2 shows the data flow path of a video decoder, which is processing NTSC, PAL, SECAM, S-Video, SCART, YPbPr, RGB, 480p and other input formats. Supporting this level of flexibility is needed in DTVs simply to allow one model to work in virtually any set-up. Typical performance characteristics of DTV decoders would include synchronization, blanking, field, active video window, horizontal and vertical syncs, clock, genlock (for downstream video encoder synchronization), host CPU interrupt and programmable logic I/O signals. This is in addition to digital video outputs, as well as methods for advanced vertical blanking interval (VBI) data retrieval. As an additional feature, some video decoders support a VBI data processor (VDP) which slices, parses and performs error-checking on teletext, closed caption (CC) and other VBI data. A built-in FIFO stores up to 11 lines of teletext data, and with proper host portsynchronization, full-screen teletext retrieval is a common requirement in several systems today. Yet some implementations require a decoder that can pass through the output formatter twice the sampled raw luma data for host-based VBI processing.
When looking at ADCs for the signal chain, features such as improved jitter-reduction performance, higher image quality in video systems, and the ability to support the increased bandwidth are needed from PC and HD video output. An 8/10-bit triple ADC providing up to 165 Msps is typical in a DTV implementation, delivering rich video performance, and is also ideal for business projectors, televisions and set-top boxes.
In the end, matching the output resolution of the video signal chain to the display's capability, as well as the resolution of the input signal, optimizes the video design. Using a lower performance front-end might have been acceptable in the days of low resolution CRT TVs. However, with the resolution of today's displays, any noise or anomalies that are in the analog front-end will be clearly visible on the DTV screen.

AUDIO
In the past, consumers may have connected a TV to their home audio system to enhance the audio experience, especially when watching movies. Advances in audio solutions, combined with the potential to place a TV in another location away from the home stereo, especially with wall mount DTVs, has driven the capability and need to integrate advanced audio solutions directly into the DTV. Also, speaker technologies have come to the point of letting you turn the entire display into a speaker element. But whether driving a surface-based or traditional speaker, the audio signal chain is crucial in maximizing the audio experience. For further differentiation in audio quality, audio processing is a must-have in DTV. Audio processing enables the standard sound modes like movie, news and music, in addition to more advanced audio features like surround-sound virtualization, bass enhancements, and other well-known audio algorithms.
Tradeoffs in an audio solution relate to the audio processing capability, audio output power, thermal dissipation and overall power consumed. Traditional audio solution consisted of two to three speakers driven by a Class-AB audio power amplifier. However, operating a Class-AB amplifier inherently generated a great deal of heat, as compared to its overall audio output. These increased high temperatures prohibited the use of Class-AB amplifiers in most thin form factor flat panel TVs because large heat sinks were required to dissipate the heat. To solve this problem, the industry adopted Class-D amplifier technology (Figure 3). Now the output field effect transistors (FET) can switch between the cut-off and the saturation regions, providing higher efficiency than Class AB amplifiers. Today, audio solutions are available you leverage a completely digital signal path. This not only maximizes audio efficiency, they can also provide effects processing and signal-to-noise ratios (SNR) greater than 110 dB.
 

 
Figure 3: Basic Class D Audio Amplifier Topology.

INTERFACE
Due to the increasing demand for making the DTV a central communication portal for the home, DTVs and set-top-boxes continue to add interfaces beyond just basic audio and video. DTVs will continue to support VGA and component video inputs (and often outputs), and even HDMI. However, DTVs also may support additional interfaces like DVI, S-Video, IEEE1394, USB and, of course, a LAN connection. Moreover, with the rapid adoption of different low power wireless interface technologies, every thing from the remote to satellite speakers can communicate easily with the DTV system " completely wirelessly!
POWER
Including the AC-to-DC conversion to create the main power for the DTV itself, most every functional block in the TV requires a particular power solution; DLP lamp, LCD bias, or backlight power for the display; core and I/O power for the main processor, DDR memory, as well as power for the tuner and video/analog signal chains. Figure 4 shows a basic power distribution flow for a DTV.
 
 

 
Figure 4: Typical DTV Power Needs
In this age of energy conservation, however, governments continually are enacting new policies and tightening existing programs to cover the standby power consumption and efficiency of consumer products. Nearly all existing programs that govern televisions are voluntary, but the prospects of mandatory requirements loom. For example, to receive an Energy Star certification, a digital television must consume less than three watts " while in standby mode. Leveraging PFC and green mode flyback converters to minimize power loss while in standby mode, several new solutions are showing up in the market. Power converters with burstmode operation at light loads, providing a signal to disable the bias power to the PFC controller during standby, are ideally suited for this application. Although decisions regarding the use of distributed power busses or local point-of-load power sources are just as critical to overall system performance.

SUMMARY
Whether HDTV continues on the path we see before us today, or jumps off onto a path where the new solution requires you to project a three-dimensional holographic image in the middle of a room, considering the entire system when making design decisions for any block in the DTV is key to optimizing the overall cost and performance of the DTV. A lower-end power solution would leave noise in the signal path that would have to be compensated for by the analog front end (AFE). Likewise, a weaker AFE attached to a high-resolution display can't take full advantage of the display technology selected. In order to maximize the experience you get when sitting in front of the DTV, the interoperability of every single block in the system is absolutely key!
ABOUT THE AUTHOR
Jonathan (Jon) Bearfield is an end equipment marketing engineer providing complete system solutions for the High Performance Analog Team in Texas Instruments. Jon has more than 20 years in the electronics industry, spread equally between end equipment development and power management semiconductors. He has a Bachelors of Science in Electrical Engineering from the State University of New York in Buffalo, and a Masters in Business Administration from the University of Texas at Austin. He can be contacted at ti_jonbearfield@list.ti.com